This invention relates to a liquid jetting apparatus wherein for example a longitudinal-mode piezoelectric vibrating member is used as an actuator.
A head member of a liquid jetting apparatus, such as a recording head of an ink-jetting recording apparatus, has a pressure-generating chamber (pressure chamber) which is communicated with a nozzle and which is partly formed by an elastic plate. A movable end of a piezoelectric vibrating member is joined to the elastic plate. The piezoelectric vibrating member can expand and contract. Thus, a volume of the pressure chamber can be changed by causing the piezoelectric vibrating member to expand and contract. As a result, ink can be supplied into the pressure chamber and a drop of the ink can be jetted from the pressure chamber.
As an actuator for driving such a recording head at a high speed, a longitudinal-mode piezoelectric vibrating member is used, which consists of alternatively stacked piezoelectric material and electric conductive layer and which can extend in a longitudinal direction thereof.
The longitudinal-mode piezoelectric vibrating member needs a smaller area in order to join to the pressure chamber than a bending-type piezoelectric vibrating member does. In addition, the longitudinal-mode piezoelectric vibrating member can be driven at a higher speed. Thus, a printing operation can be achieved with a finer resolution (definition) and at a higher speed.
However, although such a longitudinal-mode piezoelectric vibrating member can be driven at a higher speed, a reducing rate (damping rate) of remaining vibration (residual vibration) thereof is smaller. Thus, larger remaining vibration may be remained after a drop of the ink has been jetted, which may affect behavior of a meniscus of the ink. For example, if a position of the meniscus remains disordered when a next drop of the ink is jetted, the next drop of the ink may be jetted in an undesired direction. Alternatively, if the meniscus overshoots a proper range toward the nozzle so much, mist of the ink may be generated i.e. quality of printed images may be deteriorated.
Then, in order to prevent generation of the mist of the ink or the like by reducing (damping) the remaining vibration of the meniscus after the drop of the ink is jetted, the Japanese Laid-Open Publication No. 9-52360 has proposed an ink-jetting recording apparatus. The ink-jetting recording apparatus is adapted to generate a driving signal including: a first signal-element for causing a pressure chamber to expand, a second signal-element for causing the pressure chamber to contract from an expanded state thereof in order to jet a drop of the ink through a nozzle, and a third signal-element for causing the pressure chamber to expand by a volume smaller than a volume expanded by the first signal-element just when a vibration of the meniscus turns toward the nozzle after the drop of the ink is jetted. Thus, the meniscus, which is going to turn toward the nozzle after the drop of the ink is jetted, is pulled back toward the pressure chamber because the pressure chamber is caused to expand by the third signal-element. Thus, the vibration of the meniscus can be reduced effectively. Thus, the generation of the mist of the ink, which may be caused by movement of the meniscus, can be prevented. In addition, a position of the meniscus can be adjusted to a substantially regular position when a next drop of the ink is jetted, so that the next drop of the ink can be jetted more stably.
However, in the above recording apparatus, if a plurality of the drops of the ink are successively jetted at a high speed by using driving signals repeated with a short period, some pressure chambers which should not be deformed may be deformed (cross talk). Thus, meniscuses in the nozzles communicating with these pressure chambers may be caused to vibrate, although the meniscuses should not vibrate. Thus, if a meniscus in a nozzle corresponding to a pressure chamber which should not be deformed (a meniscus in a nozzle through which a drop of the ink should not be jetted) is caused to vibrate, when a drop of the ink is jetted through the nozzle in the future, the drop of the ink may be jetted unstably, for example the drop of the ink may be jetted in an undesired direction.
The object of this invention is to solve the above problems, that is, to provide a liquid jetting apparatus such as an ink-jet recording apparatus that can effectively reduce a vibration of a meniscus in a nozzle corresponding to a pressure chamber which should not be deformed in order to jet a drop of liquid more stably.
In order to achieve the object, a liquid jetting apparatus includes: a pressure chamber having an inside space whose volume is changeable, into which a liquid is supplied and which is communicated with a nozzle, a Helmholtz resonance frequency of said pressure chamber having a period of TH; a signal-generating unit that can generate a driving signal including a first signal-element for causing the pressure chamber to expand, a second signal-element for causing the pressure chamber to contract from an expanded state thereof in order to jet a drop of the liquid through the nozzle, and a third signal-element for causing the pressure chamber to expand to an original state before outputting the first signal-element after the drop of the liquid is jetted; and a pressure-generating unit that can cause the pressure chamber to expand and contract, based on the driving signal; wherein an interval between a starting time of outputting the first signal-element and a starting time of outputting the second signal-element is set substantially equal to the period TH of the Helmholtz resonance frequency; an interval between a starting time of outputting the second signal-element and a starting time of outputting the third signal-element is also set substantially equal to the period TH of the Helmholtz resonance frequency; and a sum of an amplitude of the first signal-element and an amplitude of the third signal-element is set substantially equal to an amplitude of the second signal-element.
According to the feature, the second signal-element is outputted in reverse (opposite) phase with a remaining vibration of the pressure chamber expanded by the first signal-element, and the third signal-element is outputted in reverse phase with a remaining vibration of the pressure chamber contracted by the second signal-element. In addition, a sum of the remaining vibrations of the pressure chamber expanded and contracted by the three signal-elements becomes substantially zero. That is, the first signal-element, the second signal-element and the third signal-element are outputted with respective largenesses at respective timings in such a manner that the remaining vibrations are drowned out by each other.
Thus, a deformation of a pressure chamber that should not be deformed and a vibration of a meniscus in a nozzle corresponding to the pressure chamber can be prevented effectively.
Alternatively, a liquid jetting apparatus includes: a pressure chamber having an inside space whose volume is changeable, into which a liquid is supplied and which is communicated with a nozzle, a Helmholtz resonance frequency of said pressure chamber having a period of TH; a signal-generating unit that can generate a driving signal including a first signal-element for causing the pressure chamber to expand, a second signal-element for causing the pressure chamber to contract from an expanded state thereof in order to jet a drop of the liquid through the nozzle, and a third signal-element for causing the pressure chamber to expand to an original state before outputting the first signal-element after the drop of the liquid is jetted; and a pressure-generating unit that can cause the pressure chamber to expand and contract, based on the driving signal; wherein an interval between a starting time of outputting the first signal-element and a starting time of outputting the second signal-element is set substantially equal to the period TH of the Helmholtz resonance frequency; an interval between a starting time of outputting the second signal-element and a starting time of outputting the third signal-element is also set substantially equal to the period TH of the Helmholtz resonance frequency; and durations of the first signal-element, the second signal-element and the third signal-element are set substantially equal to each other.
According to the feature, similarly, the second signal-element is outputted in reverse phase with a remaining vibration of the pressure chamber expanded by the first signal-element, and the third signal-element is outputted in reverse phase with a remaining vibration of the pressure chamber contracted by the second signal-element. In addition, a sum of the remaining vibrations of the pressure chamber expanded and contracted by the three signal-elements becomes substantially zero. That is, the first signal-element, the second signal-element and the third signal-element are outputted with respective largenesses at respective timings in such a manner that the remaining vibrations are drowned out by each other.
Thus, a deformation of a pressure chamber that should not be deformed and a vibration of a meniscus in a nozzle corresponding to the pressure chamber can be prevented effectively.
Each of the durations of the first signal-element, the second signal-element and the third signal-element can be controlled relatively easily.
Preferably, each of the durations of the first signal-element, the second signal-element and the third signal-element is set shorter than the period TH of the Helmholtz resonance frequency. In the case, the driving signal itself is shorter, so that a plurality of drops of the liquid can be jetted successively with a higher frequency.
Preferably, each of the durations of the first signal-element, the second signal-element and the third signal-element is set substantially equal to a natural period (characteristic period) TA of the pressure-generating unit. In the case, generation of remaining vibrations of the pressure-generating unit itself can be inhibited, so that the remaining vibrations of the pressure chamber can be restrained more effectively.
Preferably, the driving signal is successively generated according to a period which is substantially equal to a sum of a multiple of integer not less than three of the period TH of the Helmholtz resonance frequency and a half of the period TH of the Helmholtz resonance frequency. In the case, if the driving signal is successively generated in order to jet a plurality of drops of the liquid successively, a vibration by one driving signal and a vibration by the next driving signal may be drowned out by each other, so that the remaining vibrations can be restrained more effectively.
In order to achieve a shorter repeating period of the driving signal, the driving signal is preferably successively generated according to a period which is substantially equal to 3.5 times of the period TH of the Helmholtz resonance frequency.
In addition, preferably, the amplitude of the third signal-element is set 0.25 to 0.75 times as great as the amplitude of the second signal-element. In the case, after the drop of the liquid has been jetted, the vibration of the meniscus can be reduced (damped) by the third signal-element more effectively. Thus, generation of mist of the liquid can be prevented more effectively.
For example, the pressure-generating unit has a piezoelectric vibrating member. In order to jet a plurality of drops of the liquid successively at a high speed, it is preferable that the piezoelectric vibrating member is a longitudinal-mode piezoelectric vibrating member.
This invention is extremely effective if the period TH of the Helmholtz resonance frequency is in a range of 5 xcexcs to 20 xcexcs.
In addition, this invention is a controlling unit that can control a liquid jetting apparatus including a pressure chamber having an inside space whose volume is changeable, into which a liquid is supplied and which is communicated with a nozzle, a Helmholtz resonance frequency of said pressure chamber having a period of TH, and a pressure-generating unit that can cause the pressure chamber to expand and contract, based on a driving signal; comprising: a signal-generating unit that can generate a driving signal including a first signal-element for causing the pressure chamber to expand, a second signal-element for causing the pressure chamber to contract from an expanded state thereof in order to jet a drop of the liquid through the nozzle, and a third signal-element for causing the pressure chamber to expand to an original state before outputting the first signal-element after the drop of the liquid is jetted; wherein an interval between a starting time of outputting the first signal-element and a starting time of outputting the second signal-element is set substantially equal to the period TH of the Helmholtz resonance frequency; an interval between a starting time of outputting the second signal-element and a starting time of outputting the third signal-element is also set substantially equal to the period TH of the Helmholtz resonance frequency; and a sum of an amplitude of the first signal-element and an amplitude of the third signal-element is set substantially equal to an amplitude of the second signal-element.
Alternatively this invention is a controlling unit that can control a liquid jetting apparatus including a pressure chamber having an inside space whose volume is changeable, into which a liquid is supplied and which is communicated with a nozzle, a Helmholtz resonance frequency of said pressure chamber having a period of TH, and a pressure-generating unit that can cause the pressure chamber to expand and contract, based on a driving signal; comprising: a signal-generating unit that can generate a driving signal including a first signal-element for causing the pressure chamber to expand, a second signal-element for causing the pressure chamber to contract from an expanded state thereof in order to jet a drop of the liquid through the nozzle, and a third signal-element for causing the pressure chamber to expand to an original state before outputting the first signal-element after the drop of the liquid is jetted; wherein an interval between a starting time of outputting the first signal-element and a starting time of outputting the second signal-element is set substantially equal to the period TH of the Helmholtz resonance frequency; an interval between a starting time of outputting the second signal-element and a starting time of outputting the third signal-element is also set substantially equal to the period TH of the Helmholtz resonance frequency; and durations of the first signal-element, the second signal-element and the third signal-element are set substantially equal to each other.
A computer system can materialize the whole controlling unit or only one or more components in the controlling unit.
This invention includes a storage unit capable of being read by a computer, storing a program for materializing the controlling unit in a computer system.
This invention also includes the program itself for materializing the controlling unit in the computer system.
This invention includes a storage unit capable of being read by a computer, storing a program including a command for controlling a second program executed by a computer system including a computer, the program being executed by the computer system to control the second program to materialize the controlling unit.
This invention also includes the program itself including the command for controlling the second program executed by the computer system including the computer, the program being executed by the computer system to control the second program to materialize the controlling unit.
The storage unit may be not only a substantial object such as a floppy disk or the like, but also a network for transmitting various signals.